Ireta: a model of political and spatial organization of P'urépecha cities, The

Includes bibliographical references.2015 Summer.This thesis uses the published historical literature to build a theoretical model of the political organization of P’urépecha cities. Ancient P’urépecha cities were the urban component of a larger polity known as an Ireta. These were territorial polities that were similar to the Aztec altepetl, and might be considered analogous to a “city-state.” Each Ireta could be divided into a series of nested territorial units. Larger units, the uapátzequecha, consisted of neighborhoods within cities and towns or villages in the countryside. Beneath these were smaller groupings of households that formed the basis of the ocámbecha tax system used by the Kingdom of Tzintzuntzan, the empire which dominated the region during the Late Postclassic Period (c. 1350 – 1530 AD). Small architectural complexes (complejos) at the archaeological site of Angamuco, Michoacan, Mexico approximately match the size of the unit that the ocámbecha administered. This study maps these units using Object-Based Image Analysis (OBIA). The results of this modeling produce a map of complejos that approximately matches hypothesized territorial divisions at the site. While more research is needed, the current evidence suggests that the territorial divisions which formed the basis of the ocámbecha tax system may predate the Late Postclassic empire. This could indicate that the empire simply co-opted existing territorial divisions for tax collection rather than creating new ones

Regimes of Super-Eddington Accretion and Outflows in Extragalactic X-ray Binaries

Ultraluminous X-ray sources (ULXs) represent stellar-mass binary systems accreting at extreme rates. Their observational diversity has been attributed to numerous different physical interpretations. Here we analyse multiwavelength observations of a select number of ULXs demonstrating a wide range of contrasting observable properties. We present the discovery of the first eclipsing ULXs, a detailed study of outflows, an examination of the highest accretion-rate sources, and finally, discuss how ULX observational and physical properties might be related

Optically thick outflows in ultraluminous supersoft sources

Ultraluminous supersoft sources (ULSs) are defined by a thermal spectrum with colour temperatures ~0.1 keV, bolometric luminosities ~ a few 1039 erg s−1, and almost no emission above 1 keV. It has never been clear how they fit into the general scheme of accreting compact objects. To address this problem, we studied a sample of seven ULSs with extensive Chandra and XMM–Newton coverage. We find an anticorrelation between fitted temperatures and radii of the thermal emitter, and no correlation between bolometric luminosity and radius or temperature. We compare the physical parameters of ULSs with those of classical supersoft sources, thought to be surface-nuclear-burning white dwarfs, and of ultraluminous X-ray sources (ULXs), thought to be super-Eddington stellar-mass black holes. We argue that ULSs are the sub-class of ULXs seen through the densest wind, perhaps an extension of the soft-ultraluminous regime. We suggest that in ULSs, the massive disc outflow becomes effectively optically thick and forms a large photosphere, shrouding the inner regions from our view. Our model predicts that when the photosphere expands to ≥ 105 km and the temperature decreases below ≈50 eV, ULSs become brighter in the far-UV but undetectable in X-rays. Conversely, we find that harder emission components begin to appear in ULSs when the fitted size of the thermal emitter is smallest (interpreted as a shrinking of the photosphere). The observed short-term variability and absorption edges are also consistent with clumpy outflows. We suggest that the transition between ULXs (with a harder tail) and ULSs (with only a soft thermal component) occurs at blackbody temperatures of ≈150 eV

Discovery of two eclipsing X-ray binaries in M51

We discovered eclipses and dips in two luminous (and highly variable) X-ray sources in M 51. One (CXOM51 J132943.3+471135) is an ultraluminous supersoft source, with a thermal spectrum at a temperature of about 0.1 keV and characteristic blackbody radius of about 104 km. The other (CXOM51 J132946.1+471042) has a two-component spectrum with additional thermal-plasma emission; it approached an X-ray luminosity of 1039 erg s−1 during outbursts in 2005 and 2012. From the timing of three eclipses in a series of Chandra observations, we determine the binary period (52.75 ± 0.63 h) and eclipse fraction (22±0.1 per cent ) of CXOM51 J132946.1+471042. We also identify a blue optical counterpart in archival Hubble Space Telescope images, consistent with a massive donor star (mass of ∼20–35 M⊙). By combining the X-ray light-curve parameters with the optical constraints on the donor star, we show that the mass ratio in the system must be M2 /M1 >~ 18 and therefore the compact object is most likely a neutron star (exceeding its Eddington limit in outburst). The general significance of our result is that we illustrate one method (applicable to high-inclination sources) of identifying luminous neutron star X-ray binaries, in the absence of X-ray pulsations or phase-resolved optical spectroscopy. Finally, we discuss the different X-ray spectral appearance expected from super-Eddington neutron stars and black holes at high viewing angles

A Possible Third Body in the X-Ray System GRS 1747-312 and Models with Higher-Order Multiplicity

GRS 1747-312 is a bright Low-Mass X-ray Binary in the globular cluster Terzan 6, located at a distance of 9.5 kpc from the Earth. It exhibits regular outbursts approximately every 4.5 months, during which periodic eclipses are known to occur. These eclipses have only been observed in the outburst phase, and are not clearly seen when the source is quiescent. Recent Chandra observations of the source were performed in June 2019 and April, June, and August of 2021. Two of these observations captured the source during its outburst, and showed clear flux decreases at the expected time of eclipse. The other two observations occurred when the source was quiescent. We present the discovery of a dip that occurred during the quiescent state. The dip is of longer duration and its time of occurrence does not fit the ephemeris of the shorter eclipses. We study the physical characteristics of the dip and determine that it has all the properties of an eclipse by an object with a well defined surface. We find that there are several possibilities for the nature of the object causing the 5.3 ks eclipse. First, GRS 1747-312 may be an X-ray triple, with an LMXB orbited by an outer third object, which could be an M-dwarf, brown dwarf, or planet. Second, there could be two LMXBs in close proximity to each other, likely bound together. Whatever the true nature of the eclipser, its presence suggests that the GRS 1747-312 system is unique.Comment: 38 pages, 30 figures, submitted to MNRA